The melt-extrusion of liquids, such as, for example, thermoplastic polymers, to form fibers and nonwoven webs generally involves forcing a molten polymer through a plurality of orifices to form a plurality of molten threadlines, contacting the molten threadlines with a fluid, usually air, directed so as to form strands (filaments or fibers) and attenuate them. The attenuated strands then are randomly deposited on a surface to form a nonwoven web.
The more common and well known processes utilized for the preparation of nonwoven webs are meltblowing, coforming, and spunbonding.
Meltblowing references include, by way of example, U.S. Pat. No. 3,016,599 to Perry, Jr., U.S. Pat. No. 3,704,198 to Prentice, U.S. Pat. No. 3,755,527 to Keller et al., U.S. Pat. No. 3,849,241 to Butin et al., U.S. Pat. No. 3,978,185 to Butin et al., and U.S. Pat. No. 4,663,220 to Wisneski et al. See, also, V. A. Wente, "Superfine Thermoplastic Fibers", Industrial and Engineering Chemistry, Vol. 48, No. 8, pp. 1342-1346 (1956); V. A. Wente et al., "Manufacture of Superfine Organic Fibers", Navy Research Laboratory, Washington, D.C., NRL Report 4364 (111437), dated May 25, 1954, United States Department of Commerce, Office of Technical Services; and Robert R. Butin and Dwight T. Lohkamp, "Melt Blowing --A One-Step Web Process for New Nonwoven Products", Journal of the Technical Association of the Pulp and Paper Industry, Vol. 56, No.4, pp. 74-77 (1973).
Coforming references (i.e., references disclosing a meltblowing process in which fibers or particles are commingled with the meltblown fibers as they are formed) include U.S. Pat. No. 4,100,324 to Anderson et al. and U.S. Pat. No. 4,118,531 to Hauser.
Finally, spunbonding references include, among others, U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,655,862 to Dorschner et al., U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,705,068 to Dobo et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 3,853,651 to Porte, U.S. Pat. No. 4,064,605 to Akiyama et al., U.S. Pat. No. 4,091,140 to Harmon, U.S. Pat. No. 4,100,319 to Schwartz, U.S. Pat. No. 4,340,563 to Appel and Morman, U.S. Pat. No. 4,405,297 to Appel and Morman, U.S. Pat. No. 4,434,204 to Hartman et al., U.S. Pat. No. 4,627,811 to Greiser and Wagner, and U.S. Pat. No. 4,644,045 to Fowells.
Nonwoven webs have many uses including cleaning products such as towels and industrial wipes, personal care items such as incontinence products, infant care products, and absorbent feminine care products, and garments such as medical apparel. Polymeric strands with a high level of strength, particularly, tensile strength or tenacity, are often desirable for these applications. Typical methods of enhancing the tensile strength of a fiber or filament include increasing the denier of the fiber or filament, changing the polymer to a higher strength polymer, or adding strength enhancing ingredients to the polymer. Although these methods are often suitable, they can affect other physical properties of melt-extruded polymeric strands and nonwoven materials made therewith, such as softness and feel. Accordingly, there remains a need for melt-extruded strands and nonwovens with enhanced strength and methods of making such strands without substantially altering other physical properties of the materials.